Crosslinking between molecules of a crystalline polymer by irradiation of an active energy ray is a publicly known technology, and a crosslinking technology between molecules of a polyethylene by irradiation of an active energy ray is put to practical use as a coating layer for electric cables.
Further, it is also publicly known that a crystalline polymer shows a shape-memory effect by crosslinking. Even the active energy ray is directly irradiated to a polymer such as a polyethylene in which crosslinking is readily caused by irradiation of an active energy ray, and cleavage in the polymer chains and generation of odors are not readily caused, it is almost not problematic. However, it has been difficult to prepare a crosslinked molded article by directly irradiating to a polymer such as a polypropylene in which cleavage in the polymer chains is readily caused. Also, it is apparent that crosslinking by lower energy is preferred even in the polyethylene.
On the other hand, there has been also widely known crosslinking between molecules of a noncrystalline polymer by irradiation of an active energy ray, for example, JP-A-08059862 discloses an elevation of hardness in a polycarbonate resin and a polysulfone resin by irradiation of an active energy ray at a high temperature of approximately 150.degree. C. However, even though the noncrystalline polymer is irradiated by an active energy ray at a state of room temperatures, hardness does not change.
Crosslinking of the noncrystalline polymer requires a large amount of irradiation energy by the active energy ray, or irradiation of the active energy ray at a high temperature.
Therefore, there is a problem that there are occasionally caused cleavage of polymer chains, generation of odors, and discoloration in polymers, etc., whereby, it is not regarded as a practical crosslinking method.
In the meantime, it is known that a crystalline polymer shows a shape-memory property by crosslinking. Further, nonwoven cloth is prepared by netting a variety of synthetic fibers such as a polyester resin, a nylon resin, an aramide-based resin, an acrylic-based resin, a polyolefin-based resin, a polyurethane-based resin, a vinylon-based resin, a polyvinylchloride-based resin, a combination thereof, and moreover, natural fibers such as cotton, hemp, wool, and wooden pulp, a regenerated fibers such as rayon, and cupra, inorganic fibers such as glass, carbon, alumina, metal, and a variety of combinations thereof, from which a variety of products are prepared depending upon preparation processes to supply for a variety of uses.
However, conventional nonwoven cloth is not sufficiently satisfied in view of a recent demand for advanced functions in spite of being capable of obtaining a variety of functions depending upon selections in raw materials. For example, the nonwoven cloth in which the synthetic fibers are employed is quite beyond properties of inorganic nonwoven cloth in view of rigidity, tear strength, delamination resistance, and solvent resistance, etc.
On the other hand, although the conventional nonwoven cloth is generally more excellent in productivity and soft feel, etc., contrarily, it is poorer in strength, solvent resistance and heat resistance, etc.
In view of this background, and as a result of an extensive investigation, the inventor of this invention has now found that there can be obtained a crosslinkable polymer composition by crosslinking a specified noncrystalline polymer or a specified crystalline polymer together with a crosslinkable monomer by the irradiation of an active energy ray, whereby, crosslinked molded articles and nonwoven cloth can be obtained, in which there are improved chemical resistance, oil resistance, and scratch resistance without any loss of a variety of physical properties such as heat resistance, weatherability, and mechanical properties, and the present invention has been completed. The nonwoven cloth obtained is exceedingly excellent in rigidity, tear strength, and it shows a shape-memory property, excellent bulkiness and soft feel, resulting in that it can be employed as water-absorbable materials and filters, etc.